The invention relates to an apparatus for adjusting the tracking of the blades in a rotor, especially for a rotary wing aircraft. The term "tracking" in this context means that all blades of a multi-blade rotor, such as a helicopter rotor, rotate in the same plane when all blades are adjusted to the same blade angle and without any cyclical blade angle change.
As disclosed in German Pat. Nos. 1,531,355 and 2,150,741 rotors of this type do not require any separate mechanical flapping hinges nor any separate mechanical lead-lag hinges. Avoiding such hinges has the advantage that the useful life of such rotors is substantially increased because parts that are not needed do not break down. This feature in turn results in a smaller risk of damage. Additionally, it is possible to use the rotor hub as a protective housing, for example for the control means needed for the blade angle adjustment. Reference is made in this connection to German Pat. No. 2,658,828 in which the control rods for the blade angle adjustment are driven by a swash plate and connected to the radially inner end of the respective blade root sleeve. Such a structure for the blade angle adjustment is rather simple in a kinematic sense. However, there is no possibility for adjusting the so-called tracking through an external access to the rotor hub. After the rotor blades have been mounted to the rotor hub, such tracking of the blades relative to each other or relative to one another is desirable so that all blades may rotate in the same plane. However, to assure such tracking a fine adjustment of the blades is needed independently of the collective and uniform blade angle adjustment without regard to any cyclical blade angle adjustment.
The tracking adjustment involves a very fine adjustment of each blade about the longitudinal axis of a blade which extends in the radial direction relative to the rotational axis of the rotor. It must be possible to make the adjustment to the precise same angular degrees or even angular minutes for the individual rotor blades. Such adjustment must be possible after the original installation and also when bearings are required to be exchanged in the blade angle adjustment gear train.
German Pat. No. 3,006,088 describes a rotor with elastomeric bearings. At least one of such bearings is capable of taking up compression loads. Such rotors have the advantage that the rotor wings or blades may be tilted into a folded position. Further, such rotors also have a rotor hub functioning as a protective housing for the control mechanism used for the blade angle control.